BUG: PyMC installation fails on macOS (arm64, Homebrew Python 3.14) due to NumPy and Pytensor build incompatibility

[fcotizelati]

Describe the issue:

Attempting to install PyMC on macOS (M3, arm64) using Homebrew Python 3.14 fails during dependency resolution/build. pytensor tries to build against numpy<1.26, which has no pre-built wheels for Python 3.14, causing pip to backtrack indefinitely and then fail with:

pip._vendor.pyproject_hooks._impl.BackendUnavailable: Cannot import 'setuptools.build_meta'

Reproduceable code example:

# Create a clean environment
python3.14 -m venv pymc_test_env
source pymc_test_env/bin/activate

# Upgrade pip and attempt installation
pip install -U pip setuptools wheel
pip install pymc

Error message:

Collecting pymc
  Using cached pymc-5.26.1-py3-none-any.whl
...
ERROR: subprocess-exited-with-error
pip._vendor.pyproject_hooks._impl.BackendUnavailable: Cannot import 'setuptools.build_meta'

PyMC version information:

PyMC/PyMC3 Version: attempted installation of pymc==5.26.1 (installation failed)

PyTensor/Aesara Version: not installed (build failed for pytensor==2.17.1)

Python Version: 3.14.0 (Homebrew build, arm64)

Context for the issue:

No response

[ricardoV94]

We don't yet support python 3.14 officially, but the numpy<2 is coming from somewhere else. We only support numpy>2.0 in the latest releases of pymc and pytensor

[ricardoV94]

Can you share more of the error? The last line is not enough to infer much. Also note our official instructions are to use conda, not pip: https://www.pymc.io/projects/docs/en/stable/installation.html

As PyMC/PyTensor require cython/C compilers that can't be handled by pip

[fcotizelati]

@ricardoV94 thanks for the quick reply!
Indeed, this is under Python 3.14.0 (Homebrew, arm64), so that explains part of it.

I'm attaching a longer excerpt from the build log. It looks like the issue is triggered when pytensor’s pyproject.toml specifies numpy<1.26, which forces pip to build NumPy 1.25 from source (no wheels yet for 3.14). That isolated build environment pulls an older setuptools/pkg_resources, which fails with ImpImporter(removed in Python 3.12+).

pymc_build.log

[ricardoV94]

That PyTensor version is ancient, install 2.35.1 first. Current pymc is definitely not compatible with that PyTensor version

[fcotizelati]

Trying to install pytensor==2.35.1 fails before resolution due to Requires-Python markers.
pip lists recent PyTensor releases as <3.14 (e.g. 2.35.0 has >=3.11,<3.14), so 3.14 is excluded and only ancient versions (e.g. 2.17.1) remain candidates.

$ python3.14 -m pip index versions pytensor | sed -n '1,40p'
pytensor (2.17.1)
Available versions: 2.17.1, 2.17.0, 2.16.3, 2.16.2, 2.16.1, 2.16.0, 2.15.0, 2.14.2, 2.14.1, 2.14.0, 2.13.1, 2.13.0, 2.12.3, 2.12.2, 2.12.1, 2.12.0, 2.11.2, 2.11.1, 2.11.0, 2.10.1, 2.10.0, 2.9.1, 2.8.11, 2.8.10

[ricardoV94]

That explains it. The very old version didn't have the explicit pin. The newer ones have. There's a PR to lift the pin in pymc-devs/pytensor#1661

Otherwise you can try to install locally and remove the pin manually but if you can wait 1-2 weeks and it should be available without hacks

[fcotizelati]

Got it, thanks. No problem, I can wait until the pin is lifted in the next release. I’ll re-test once the updated PyTensor is available.